Be careful whose advice you buy, but be patient with those who supply it. Advice is a form of nostalgia, dispensing it is a way of fishing the past from the disposal, wiping it off, painting over the ugly parts and recycling it for more than its worth ~ Baz Luhrmann - Everybody's Free (To Wear Sunscreen)

I sent some mail headers to the tech at FORTIGATE, he says that it looks to him like the SMEServer is using encryption when it can, and their filter can't filter ESMTP.

If Fortigate know so little about SMTP, then I really wonder how good their appliance is.

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He asked me if there was a way we could set the SMEServer to only accept SMTP.Is that possible?

If their applianace says "HELO appliance.domain.name" then SME will reply using pure SMTP syntax. If their appliance says "EHLO appliance.domain.name" then SME will reply using ESMTP syntax. This is standard behaviour. Google for "ESMTP RFC" and you, and they, can read all the details.